Recently, from the perspective of preserving the environment, a wind turbine generator utilizing wind energy has been attracting attention. The wind turbine generator generally includes a rotor where a plurality of blades is attached to a hub. The rotor is mounted to a nacelle disposed atop a tower provided upright onshore or offshore. In this type of wind turbine generator, the rotor rotates upon receiving wind at the blades, the rotation of the rotor is transmitted to a generator housed in the nacelle, and then electrical power is generated in the generator.
In such a wind turbine generator, the direction of the rotor is normally changed in accordance with the wind direction in order to efficiently convert the wind energy to the rotational energy of the rotor. Thus, there is known a wind turbine generator including a yaw drive mechanism for rotating the nacelle to which the rotor is supported. For instance, Patent Document 1 describes a yaw rotation control method of controlling the yaw direction of the nacelle so that the rotor rotational plane faces the wind direction according to the wind direction deviation between the direction of the nacelle and the actual wind direction.
Further, Patent Document 2 discloses a configuration for stopping the yaw rotation upon detecting that the yaw direction of a wind turbine generator has come out of the operating range with a potentiometer for detecting the yaw direction of a wind turbine generator.